Etching method

ABSTRACT

A method for selectively etching a first region of silicon oxide with respect to a second region of silicon nitride, includes: preparing a target object including the first region and the second region in a processing chamber of a plasma processing apparatus; and generating a plasma of a processing gas containing a fluorocarbon gas and a rare gas in the processing chamber. In the generating the plasma of the processing gas, a self-bias potential of a lower electrode on which the target object is mounted is greater than or equal to 4V and smaller than or equal to 350V and a flow rate of the rare gas in the processing gas is 250 to 5000 times of a flow rate of the fluorocarbon gas in the processing gas.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/202,356,filed Jul. 5, 2016 which claims priority to Japanese Patent ApplicationNo. 2015-135905 filed on Jul. 7, 2015, the disclosures of which areincorporated herein in their entirety by reference, and priority isclaimed to each of the foregoing.

FIELD OF THE INVENTION

The disclosure relates to an etching method; and more particularly, to amethod for selectively etching a first region of silicon oxide withrespect to a second region of silicon nitride.

BACKGROUND OF THE INVENTION

In manufacturing electronic devices, the first region of silicon oxideis selectively etched with respect to the second region of siliconnitride. In this etching process, a plasma of a processing gascontaining a fluorocarbon gas, argon gas and oxygen gas is generated ina processing chamber of a plasma processing apparatus, as disclosed in,e.g., Japanese Patent Application Publication No. 2002-25979.

A SAC (Self-Aligned Contact) technique is known as a technique forselectively etching the first region with respect to the second region.In the SAC technique, the first region in a recess formed by the secondregion is etched in a self-aligned manner. In the SAC technique, theaforementioned processing gas is used and a plasma of the processing gasis generated in the processing chamber.

In the above-described technique, the second region is considerablyetched when the first region is etched. Therefore, it is required toetch the first region of silicon oxide while suppressing etching of thesecond region of silicon nitride.

SUMMARY OF THE INVENTION

In accordance with an aspect, there is provided a method for selectivelyetching a first region of silicon oxide with respect to a second regionof silicon nitride. The method includes: preparing a target objectincluding the first region and the second region in a processing chamberof a plasma processing apparatus; and generating a plasma of aprocessing gas containing a fluorocarbon gas and a rare gas in theprocessing chamber. In the generating the plasma of the processing gas,a self-bias potential of a lower electrode on which the target object ismounted is greater than or equal to 4V and smaller than or equal to 350Vand a flow rate of the rare gas in the processing gas is 250 to 5000times of a flow rate of the fluorocarbon gas in the processing gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the disclosure will become apparent from thefollowing description of embodiments, given in conjunction with theaccompanying drawings, in which:

FIG. 1 is a flowchart showing an etching method according to anembodiment;

FIG. 2 is a partially enlarged cross sectional view of an example of atarget object to be processed;

FIG. 3 schematically shows an example of a plasma processing apparatus;

FIG. 4 shows an example of a gas supply unit;

FIG. 5 shows another example of the gas supply unit;

FIG. 6 shows a still another example of the gas supply unit;

FIGS. 7 to 9 are partially enlarged cross sectional views of the targetobject during implementation of the method shown in FIG. 1;

FIG. 10 is a partially enlarged cross sectional view of the targetobject after the implementation of the method shown in FIG. 1;

FIG. 11 is a flowchart showing an etching method according to anotherembodiment;

FIGS. 12 to 15 are partially enlarged cross sectional views of thetarget object during implementation of the method shown in FIG. 11; and

FIGS. 16A and 16B are views for explaining test examples 1 to 3 andcomparative examples 1 and 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments will be described in detail with reference tothe accompanying drawings. Further, like reference numerals will be usedfor like parts throughout the respective drawings.

FIG. 1 is a flowchart showing an etching method according to anembodiment. A method MT shown in FIG. 1 is a method for selectivelyetching a first region of silicon oxide with respect to a second regionof silicon nitride.

FIG. 2 is a partially enlarged cross sectional view of an example of atarget object to be processed. As shown in FIG. 2, the target object(hereinafter, referred to as “wafer W”) includes a substrate SB, a firstregion R1, a second region R2, and an organic film OL that will become amask later. For example, the wafer W is obtained during themanufacturing process of a fin-type field effect transistor and furtherincludes a protruding region RA, a silicon-containing anti-reflectionfilm AL, and a resist mask RM.

The protruding region RA protrudes from the substrate SB. The protrudingregion RA may serve as, e.g., a gate region. The second region R2 ismade of silicon nitride (Si₃N₄) and formed on surfaces of the protrudingregion RA and the substrate SB. As shown in FIG. 2, the second regionR2, extends to form a recess. For example, the recess has a depth ofabout 150 nm and a width of about 20 nm.

The first region R1 is made of silicon oxide (SiO₂) and formed on thesecond region R2. Specifically, the first region R1 fills the recessformed by the second region R2 and covers the second region R2.

The organic film OL is formed on the first region R1. The organic filmOL may be made of an organic material, e.g., amorphous carbon. Theanti-reflection film AL is formed on the organic film OL. The resistmask RM is formed on the anti-reflection film AL. The resist mask RMprovides an opening having a width greater than that of the recessformed by the second region R2. The opening of the resist mask RM has awidth of, e.g., about 60 nm. A pattern of the resist mask RM is formedby a photolithography technique.

In the method MT, the target object such as the wafer W shown in FIG. 2is processed in a plasma processing apparatus. FIG. 3 schematicallyshows an example of the plasma processing apparatus. The plasmaprocessing apparatus 10 shown in FIG. 3 is configured as a capacitivelycoupled plasma etching apparatus and includes a substantiallycylindrical processing chamber 12. The processing chamber 12 is made of,e.g., aluminum, and an inner wall surface of the processing chamber 12is anodically oxidized. The processing chamber 12 is frame-grounded.

A substantially cylindrical supporting part 14 is provided at a bottomportion of the processing chamber 12. The supporting part 14 is made of,e.g., an insulating material. In the processing chamber 12, thesupporting part extends vertically from the bottom portion of theprocessing chamber 12. Further, in the processing chamber 12, a mountingtable PD is provided. The mounting table PD is supported by thesupporting part 14.

The wafer W is held on a top surface of the mounting table PD. Themounting table PD includes a lower electrode LE and an electrostaticchuck ESC. The lower electrode LE has a first plate 18 a and a secondplate 18 b. The first plate 18 a and the second plate 18 b are made of ametal, e.g., aluminum, and have a substantially disc shape. The secondplate 18 b is provided on the first plate 18 a and electricallyconnected to the first plate 13 a.

The electrostatic chuck ESC is provided on the second plate 18 b. Theelectrostatic chuck ESC has a structure in which an electrode made of aconductive film is interposed between two insulating layers or twoinsulating sheets. A DC power supply 22 is electrically connected to theelectrode of the electrostatic chuck ESC through a switch 23. The waferW is attracted and held on the electrostatic chuck ESC by anelectrostatic force such as a Coulomb force or the like generated by aDC voltage applied from the DC power supply 22.

A focus ring FR is provided on a peripheral portion of the second plate18 b to surround an edge of the wafer W and the electrostatic chuck ESC.The focus ring FR is provided to improve uniformity of etching. Thefocus ring FR is made of a material that is appropriately selecteddepending on a material of an etching target film. For example, thefocus ring FR may be made of quartz.

A coolant path 24 is provided in the second plate 18 b. The coolant path24 constitutes a temperature control mechanism. A coolant is supplied tothe coolant path 24 from an external chiller unit through a line 26 a.The coolant flowing in the coolant path 24 returns to the chiller unitthrough a line 26 b. The coolant circulates between the coolant path 24and the chiller. A temperature of the wafer W held on the electrostaticchuck ESC is controlled by controlling a temperature of the coolant.

The plasma processing apparatus 10 further includes a gas supply line28. A heat transfer gas supply unit (not shown) supplies a heat transfergas, e.g., He gas to a gap between a top surface of the electrostaticchuck ESC and a backside of the wafer W through the gas supply line 28.

The plasma processing apparatus 10 further includes an upper electrode30. The upper electrode 30 is provided above the mounting table PD toface the mounting table PD. The upper electrode 30 and the lowerelectrode LE are approximately parallel to each other. Between the upperelectrode 30 and the mounting table PD, a processing space S whereplasma processing is performed on the wafer W is defined.

The upper electrode 30 is held at an upper portion of the processingchamber 12 through an insulating shield member 32. In the presentembodiment, the upper electrode 30 may be configured such that avertical distance from the top surface of the mounting table PD, i.e., awafer mounting surface, to the upper electrode 30 is variable. The upperelectrode 30 may include a top plate 34 and a holding body 36. The topplate 34 is in contact with the space S and has a plurality of gasinjection openings 34 a. In the present embodiment, the top plate 34 ismade of silicon.

The holding body 36 detachably holds the top plate 34 and is made of aconductive material, e.g., aluminum. The holding body 36 may have awater cooling structure. A gas diffusion space 36 a is provided in theholding body 36. A plurality of gas passage holes 36 b communicatingwith the gas injection openings 34 a extends downward from the gasdiffusion space 36 a. Further, the holding body 36 includes a gas inletport 36 c for guiding a processing gas into the gas diffusion space 36a. A gas supply line 38 is connected to the gas inlet port 36 c.

The gas supply line 38 is connected to a gas supply unit GU. FIG. 4shows an example of the gas supply unit. The first exemplary gas supplyunit GU shown in FIG. 4 includes a gas source group GSG, a valve group42, a flow rate controller group 43, and a valve group 44. In the firstexemplary gas supply unit GU, the gas source group GSG includes aplurality of gas sources GS1 to GS7; the valve group 42 includes aplurality of valves 421 to 427; the flow rate controller group 43includes a plurality of flow rate controllers 431 to 437; and the valvegroup 44 includes a plurality of valves 441 to 447. Further, each of theflow rate controllers 431 to 437 is a mass flow controller or apressure-controlled flow rate controller.

The gas source GS1 is a source of C₄F₈ gas and is connected to the gassupply line 38 via the valve 421, the flow rate controller 431, and thevalve 441. The gas source GS2 is a source of CF₄ gas and is connected tothe gas supply line 38 via the valve 422, the flow rate controller 432,and the valve 442. The gas source GS3 is a source of C₄F₆ gas and isconnected to the gas supply line 38 via the valve 423, the flow ratecontroller 433, and the valve 443. The gas source GS4 is a source of arare gas and is connected to the gas supply line 38 via the valve 424,the flow rate controller 434, and the valve 444. The rare gas may be anyrare gas such as He gas, Ne gas, Ar gas or Kr gas. The gas source GS5 isa source of nitrogen gas (N₂ gas) and is connected to the gas supplyline 38 via the valve 425, the flow rate controller 435, and the valve445. The gas source GS6 is a source of hydrogen gas (H₂ gas) and isconnected to the gas supply line 38 via the valve 426, the flow ratecontroller 436, and the valve 446. The gas source GS7 is a source ofoxygen gas (O₂ gas) and is connected to the gas supply source 38 via thevalve 427, the flow rate controller 437, and the valve 447. The firstexemplary gas supply unit GU may further include a source of anoxygen-containing gas, e.g., a source of a carbon oxide gas, and valvesand a flow rate controller which are provided between the correspondingsource and the gas supply line 38.

The first exemplary gas supply unit GU includes a plurality of gassources for a plurality of different single gases and is configured tocontrol a flow rate of a gas from selected one or more gas sources andsupply the gas at the controlled flow rate to the gas supply line 38.

FIG. 5 shows another example of the gas supply unit. In the secondexemplary gas supply unit GU shown in FIG. 5, the gas source group GSGincludes a gas source GS8 in addition to the aforementioned gas sourcesGS1 to GS7. In the second exemplary gas supply unit GU, the valve group42 further includes a valve 428; the flow rate controller group furtherincludes a flow rate controller 438; and the valve group 44 furtherincludes a valve 448. The second exemplary gas supply unit GU mayfurther include a source of an oxygen-containing gas, e.g., a source ofa carbon oxide gas, and valves and a flow rate controller which areprovided between the source and the gas supply line 38.

The gas source GS8 is a source of a gaseous mixture of a fluorocarbongas and a rare gas, i.e., a source of a first gas. The fluorocarbon gasis, e.g., C₄F₆ gas. The rare gas is any rare gas as described above. Thegas source GS8 is connected to the gas supply line 38 via the valve 428,the flow rate controller 438, and the valve 448. The gas from the gassource GS8 may be used in a step ST4 to be described later. Theprocessing gas used in the step ST4 is obtained by diluting afluorocarbon gas with a rare gas having a large flow rate. Therefore,the flow rate of the fluorocarbon gas in the total flow rate of theprocessing gas is considerably small. When the fluorocarbon gas havingsuch a flow rate is supplied from a gas source of a single gas, the flowrate controller requires a high accuracy. Meanwhile, in the secondexemplary gas supply unit GU, there is used a single gas source GS8 fora mixed gas of a fluorocarbon gas of a desired flow rate and a rare gasof a desired flow rate. Accordingly, in the second exemplary gas supplyunit GU, it is possible to supply the fluorocarbon gas at a desired flowrate and the rare gas at a desired flow rate without using a flow ratecontroller having a high accuracy.

FIG. 6 shows a still another example of the gas supply unit. In a thirdexemplary gas supply unit GU shown in FIG. 6, a gas source group GSGincludes a gas source GS9 in addition to the aforementioned gas sourcesGS1 to GS8. In the second gas supply unit GU, the valve group 42 furtherincludes a valve 429; the flow rate controller group 43 further includesa flow rate controller 439; and the valve group 44 further includes avalve 449. The third gas supply unit GU may further include a source ofan oxygen-containing gas, e.g., a source of a carbon oxide gas, andvalves and a flow rate controller which are provided between thecorresponding source and the gas supply line 38.

The gas source GS9 is a source of a second gas. The second gas includesonly a rare gas or includes a fluorocarbon gas and a rare gas. When thesecond gas includes a fluorocarbon gas and a rare gas, the volume ratioof the fluorocarbon gas and the rare gas in the gas source GS9 isdifferent from that of the first gas in the gas source GS8. The gassource GS8 and the gas source GS9 of the third exemplary gas supply unitGU are used to supply the processing gas in the step ST4. In this step,the flow rate of the first gas of the gas source GS8 and the flow rateof the second gas of the gas source GS9 are controlled depending on adesired flow rate of the fluorocarbon gas and a desired flow rate of therare gas. Accordingly, the flow rate of the fluorocarbon gas in theprocessing gas can be controlled with a high resolution without using aflow rate controller having a high accuracy.

For example, it is assumed that the first gas of the gas source GS8includes a fluorocarbon gas and a rare gas at a volume ratio of0.1%:99.9% and the second gas of the gas source GS9 includes only a raregas. In this case, if the flow rate of the first gas is controlled to500 sccm and the flow rate of the second gas is controlled to 500 sccm,the flow rate of the rare gas becomes about 1000 sccm and the flow rateof the fluorocarbon gas becomes 0.5 sccm. Further, if the flow rate ofthe first gas is controlled to 490 sccm and the flow rate of the secondgas is controlled to 510 sccm, the flow rate of the rare gas becomesabout 1000 sccm and the flow rate of the fluorocarbon gas becomes 0.49sccm. Even if the resolution in controlling the flow rate of the firstgas of the gas source GS8 and the flow rate of the second gas of the gassource GS9 is low, it is possible to control the flow rate of thefluorocarbon gas with a high resolution.

Referring back to FIG. 3, in the plasma processing apparatus 10, adeposition shield 46 is detachably provided along the inner wall of theprocessing chamber 12. The deposition shield 46 is also provided at anouter periphery of the supporting part 14. The deposition shield 46prevents an etching by-product (deposit) from being adhered to theprocessing chamber 12. The deposition shield 46 may be made of aluminumcoated with ceramic such as Y₂O₃ or the like.

A gas exhaust plate 48 is provided at a lower portion in the processingchamber 12 and between the supporting part and the sidewall of theprocessing chamber 12. A plurality of through-holes is formed throughthe gas exhaust plate 48 in a thickness direction thereof. The gasexhaust plate 48 may be formed by coating aluminum with ceramic, e.g.,Y₂O₃ or the like. In the processing chamber 12, a gas exhaust port 12 eis provided below the gas exhaust plate 48. A gas exhaust unit 50 isconnected to the gas exhaust port 12 e through a gas exhaust line 52.The gas exhaust unit 50 has a vacuum pump such as a turbo molecular pumpor the like, and can depressurize the space in the processing chamber 12to a predetermined vacuum level. A loading/unloading port 12 g for thewafer W is provided at the sidewall of the processing chamber 12. Theloading/unloading port 12 g can be opened and closed by a gate valve 54.

The plasma processing apparatus 10 further includes a first highfrequency power supply 62 and a second high frequency power supply 64.The first high frequency power supply 62 generates a high frequencypower for plasma generation, e.g., a high frequency power having afrequency in a range from 27 MHz to 100 MHz. The first high frequencypower supply 62 is connected to the lower electrode LE through amatching unit 66. The matching unit 66 has a circuit for matching anoutput impedance of the first high frequency power supply 62 with aninput impedance of the load side (the lower electrode LE side). Thefirst high frequency power supply 62 may be connected to the upperelectrode 30 through the matching unit 66.

The second high frequency power supply 64 generates a high frequencybias power for ion attraction to the wafer W, e.g., a high frequencybias power having a frequency in a range from 400 kHz to 13.56 MHz. Thesecond high frequency power supply 64 is connected to the lowerelectrode LE through a matching unit 68. The matching unit 68 has acircuit for matching an output impedance of the second high frequencypower supply 64 with an input impedance of the load side (the lowerelectrode LE side).

The plasma processing apparatus 10 further includes a power supply 70.The power supply 70 is connected to the upper electrode 30. The powersupply 70 applies to the upper electrode 30 a voltage for attractingpositive ions in the processing space S to the top plate 34. In thisexample, the power supply 70 is a DC power supply for generating anegative DC voltage. In another example, the power supply 70 may be anAC power supply for generating an AC voltage having a relatively lowfrequency. The voltage applied from the power supply 70 to the upperelectrode 30 may be lower than or equal to −150V. In other words, thevoltage applied from the power supply 70 to the upper electrode 30 maybe a negative voltage having an absolute value of 150 or above. Whensuch a voltage is applied from the power supply 70 to the upperelectrode 30, the positive ions in the processing space S collide withthe top plate 34. Accordingly, secondary electrons and/or silicon areemitted from the top plate 34. The emitted silicon is combined withactive species of fluorine in the processing space S, so that the amountof active species of fluorine is decreased.

In the present embodiment, the plasma processing apparatus 10 mayfurther include a control unit Cnt. The control unit Cnt is a computerincluding a processor, a storage unit, an input device, a display deviceand the like. The control unit Cnt controls the respective components ofthe plasma processing apparatus 10. The control unit Cnt can allow anoperator to input commands to manage the plasma processing apparatus 10by using the input device and display the operation state of the plasmaprocessing apparatus 10 on the display device. The storage unit of thecontrol unit Cnt stores therein a control program for controllingvarious processes performed in the plasma processing apparatus 10, and aprogram, i.e., a processing recipe, for performing processes of therespective components of the plasma processing apparatus 10 based on theprocessing conditions.

Hereinafter, the method MT will be described in detail with reference toFIG. 1. Hereinafter, FIGS. 2 and 7 to 10 will be appropriately referredto together with FIG. 1. FIGS. 7 to 9 are partially enlarged crosssectional views of the target object during the implementation of themethod shown in FIG. 1. FIG. 10 is a partially enlarged cross sectionalview of the target object after the implementation of the method shownin FIG. 1. In the following, an example in which the wafer W shown inFIG. 2 is processed by the method MT by using a single plasma processingapparatus 10 shown in FIG. 3 will be described. In the respective stepsof the method MT implemented by using the plasma processing apparatus10, the operations of the respective units of the plasma processingapparatus 10 can be controlled by the control unit Cnt.

First, a step ST1 of the method MT is executed. In the step ST1, thewafer W shown in FIG. 2 is prepared in the processing chamber 12 of theplasma processing apparatus 10. Specifically, the wafer W is loaded intothe processing chamber 12 to be mounted on the mounting table PD andheld thereon by the electrostatic chuck ES of the mounting table PD.

Next, a step ST2 of the method MT is executed. In the ST2, theanti-reflection film AL is etched. To that end, a processing gas issupplied into the processing chamber 12 from a gas source selected amongthe gas sources of the gas source group GSG. This processing gasincludes a fluorocarbon gas. The fluorocarbon gas may contain, e.g., atleast one of C₄F₈ gas and CF₄ gas. The processing gas may furtherinclude a rare gas, e.g., Ar gas. In the step ST2, a pressure in theprocessing chamber 12 is set to a predetermined level by the operationof the gas exhaust unit 50. In the step ST2, the high frequency powerfrom the first high frequency power supply 62 and the high frequencybias power from the second high frequency power supply 64 are suppliedto the lower electrode LE.

In the step ST2, the plasma of the processing gas is generated and aportion of the anti-reflection film AL which is exposed through theopening of the resist mask RM is etched by active species of fluorineand/or fluorocarbon. As result, the portion of the anti reflection filmAI which is exposed through the opening of the resist mask RM is removedas can be seen from FIG. 1. In other words, a pattern of the resist maskRM is transferred to the anti-reflection film AL and the anti-reflectionfilm AL is formed to have a pattern providing an opening.

Next, in a step ST3, the organic film OL is etched. To that end, aprocessing gas is supplied into the processing chamber 12 from a gassource selected among the gas sources of the gas source group GSG. Thisprocessing gas may include hydrogen gas and nitrogen gas. Moreover, theprocessing gas used in the step ST3 may contain another gas, e.g.,oxygen gas, as long as it can etch the organic film. In the step ST3, apressure in the processing chamber 12 is set to a predetermined level bythe operation of the gas exhaust unit 50. In the step ST3, the highfrequency power from the first high frequency power supply 62 and thehigh frequency bias power from the second high frequency power supply 64are supplied to the lower electrode LE.

In the step ST3, the plasma of the processing gas is generated and aportion of the organic film at which exposed through the opening of theanti-reflection film AL is etched. The resist mask RM is also etched. Asa result, the resist mask RM is removed and the portion of the organicfilm OL which is exposed through the opening of the anti-reflection filmAL is removed, as can be seen from FIG. 8 In other words, the pattern ofthe anti-reflection film AL is transferred to the organic film CL andthe organic film CL is formed to have a pattern providing an opening MO,thereby serving as a mask MK.

Then, in the step ST4, the first region R1 is etched To that end, thestep ST4, a plasma of a processing gas is generated in the processingchamber 12. This processing gas includes a fluorocarbon gas and a raregas. The fluorocarbon gas is, e.g., C₄F₆ gas. The rare gas is, e.g., Argas. In the present embodiment, the processing gas further includesoxygen gas. Since the oxygen gas is included in the processing gas, theamount of deposit DP to be described later is appropriately controlled.

In the step ST4, the processing gas is supplied into the processingchamber 12 from a gas source selected among the gas sources of the gassource group GSG. In the present embodiment, the processing gas issupplied by any one of the first to the third exemplary gas supply unitsGU. In the case of using the second gas supply unit GU, the gaseousmixture of a fluorocarbon gas and a rare gas is supplied from the gassource GS8. In the case of using the third exemplary gas supply unit GU,the first gas including a fluorocarbon gas and a rare gas is suppliedfrom the gas source GS8 (first gas source) and the second gas includingonly a rare gas or including a fluorocarbon gas and a rare gas at avolume ratio different from that of the first gas is supplied from thegas source GS9 (second gas source). In the step ST4, a pressure in theprocessing chamber 12 is set to a predetermined level by the operationof the gas exhaust unit 50. Further, in the step ST4, the high frequencypower from the first high frequency power supply 62 is supplied to thelower electrode LE. In the step ST4, the high frequency bias power fromthe second high frequency power supply 64 may or may not be supplied tothe lower electrode LE.

In the step ST4, the high frequency power from the first high frequencypower supply 62 is set such that the self-bias potential of the lowerelectrode LE on which the wafer W is mounted becomes greater than orequal to 4V and smaller than or equal to 350V. When the high frequencybias power from the second high frequency power supply 64 as well as thehigh frequency power from the first high frequency power supply 162 aresupplied to the lower electrode LE, both of the high frequency powerfrom the first high frequency power supply 62 and the high frequencybias power from the second high frequency power supply 64 are set suchthat the self-bias potential is generated. The self-bias potential tendsto be increased as the high frequency power from the first highfrequency power supply 62 is increased and as the high frequency biaspower from the second high frequency power supply 64 is increased.Further, the self-bias potential depends on the pressure in the space inthe processing chamber 12, the frequency of the high frequency power ofthe first high frequency power supply 62, and the frequency of the highfrequency bias power from the second high frequency power supply 64.When the pressure in the space in the processing chamber 12, thefrequency of the high frequency power of the first high frequency powersupply 62, the frequency of the high frequency bias power from thesecond high frequency power supply 64 and the like are determined, theself-bias potential can be set to a desired value by controlling thehigh frequency power from the first high frequency power supply 62 andthe high frequency bias power from the second high frequency powersupply 64 in accordance with the above-described tendency.

Further, in the step ST4, the flow rate of the rare gas in theprocessing gas is set to be 250 to 5000 times of the flow rate of thefluorocarbon gas in the processing gas. In other words, a fluorocarbongas diluted with a large amount of rare gas is used in the step ST4.

The step ST4 is executed under the following processing condition.

-   Pressure in processing chamber: 10 mTorr (1.33 Pa) to 100 mTorr    (13.3 Pa)-   Processing gas

C₄F₆ gas: 0.2 sccm to 4 sccm

Ar gas: 500 sccm to 1500 sccm

O₂ gas: 0.2 sccm to 5 sccm

-   High frequency power for plasma generation: 30 W to 500 W-   High frequency bias power: 0 W to 100 W-   Negative DC voltage of power supply 70: 0V to −600V

In the step ST4, the first region R1 is etched by active species offluorocarbon and/or fluorine obtained by generating a plasma of theprocessing gas, as shown in FIG. 9. Further, a deposit DP containingfluorocarbon and/or carbon is formed on the surface of the mask MK, theside surface defining the opening obtained by the etching, and thesurface of the second region R2. The first region R1 is etched in astate where the second region R2 is protected by the deposit DP. Whenthe step ST4 is completed, the first region R1 is etched to the bottomsurface of the recess formed by the second region R2 as shown in FIG.10.

In the step ST4 of the method MT, the fluorocarbon gas in the processinggas is diluted with a large amount of the rare gas and the self-biaspotential is greater than or equal to 4V and lower than or equal to350V, the erosion of the second region R2 is suppressed during theetching of the first region R1.

When the self-bias potential of the lower electrode LE is set to be 4Vor above, the energy of the ions irradiated to the wafer W becomes 4 eVor above. When the ions having the energy of 4 eV or above areirradiated to the wafer W, the bond between silicon and oxygen formingthe first region R1 is broken, thereby generating a reaction by-productof silicon and fluorine. The reaction by-product thus generated isdischarged. When the self-bias potential of the lower electrode LE isset to 350V or less, the energy of ions irradiated to the wafer Wbecomes slightly greater than 350 eV. The ions having such energy do notpenetrate through the deposit DP having a thickness of 2 nm. Therefore,when the self-bias potential is smaller than or equal to 350V, theerosion of the second region R2 is suppressed. When the fluorocarbon gasin the processing gas used in the step ST4 is diluted with the dilutiongas of which flow rate is 250 to 5000 times greater than that of thefluorocarbon gas, the erosion of the second region R2 can be furthersuppressed while allowing the etching of the first region R1. This isconsidered because the amount of fluorine in the deposit DP is reducedand a relatively hard deposit DP is formed on the second region R2.

Hereinafter, an etching method according to another embodiment will bedescribed. FIG. 11 is a flowchart showing an etching method according toanother embodiment. A method MT2 shown in FIG. 11 is different from themethod MT in that it includes a sequence SQ. The method MT2 may furtherinclude a step ST5. Hereinafter, FIGS. 12 to 15 will be referred to inaddition to FIG. 11. FIGS. 12 to 15 are partially enlarged crosssectional views of the target object during implementation of the methodshown in FIG. 11. In the following, an example in which the wafer Wshown in FIG. 2 is processed by the method MT2 by using a single plasmaprocessing apparatus 10 will be described. In each step of the methodMT2 implemented by using the plasma processing apparatus 10, theoperations of the respective units of the plasma processing apparatus 10can be controlled by the control unit Cnt.

In the method MT2, the steps ST1 to ST3 are executed as in the case ofthe method MT and the wafer W having a state shown in FIG. 8 isobtained. Next, a step ST5 is executed. In the step ST5, the firstregion R1 is etched until immediately before the second region R2 isexposed. In other words, the first region R1 is etched until the firstregion R1 remains a little on the second region R2. To that end, in thestep ST5, a processing gas is supplied into the processing chamber 12from a gas source selected among the gas sources of the gas source groupGSG. This processing gas includes a fluorocarbon gas. The processing gasmay further include a rare gas, e.g., Ar gas. The processing gas mayfurther include oxygen gas. In the step ST5, a pressure in theprocessing chamber 12 is set to a predetermined level by the operationof the gas exhaust unit 50. Moreover, in the step ST5, the highfrequency power from the first high frequency power supply 62 and thehigh frequency bias power from the second high frequency power supply 64are supplied to the lower electrode LE.

As shown in FIG. 12, in the step ST5, the plasma of the processing gasis generated and a portion of the first region R1 which is exposedthrough the opening of the mask MK is etched by active species offluorine and/or fluorocarbon. Further, in the step ST5, the deposit DPcontaining fluorocarbon and/or carbon is formed on the surface of themask MK and the side surface defining the opening obtained by theetching. The processing time in the step ST5 is set such that apredetermined thickness of the first region R1 remains on the secondregion R2 when the step ST5 is completed.

The processing condition of the step ST5 may be identical to that of thestep ST4. Or, the step ST5 may be executed under the followingprocessing condition such that the etching of the first region R1 can beperformed within a shorter period of time.

-   Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65    Pa)-   Processing gas

C₄F₈ gas: 10 sccm to 30 sccm

CF₄ gas: 50 sccm to 150 sccm

Ar gas: 500 sccm to 1000 sccm

O₂ gas: 10 sccm to 30 sccm

-   High frequency power for plasma generation: 500 W to 2000 W-   High frequency bias power: 500 W to 2000 W

Next, in the method MT2, the sequence SQ is executed at least once. Thesequence SQ is executed to etch the first region R1 in a periodincluding a time when the second region R2 is exposed. The sequence SQincludes steps ST11 and ST13. In the present embodiment, the sequence SQmay further include a step ST12.

In the step ST11, the plasma of the processing gas is generated in theprocessing chamber 12 where the wafer W shown in FIG. 12 isaccommodated. To that end, in the step ST11, a processing gas issupplied into the processing chamber 12 from a gas source selected amongthe gas sources of the gas source group GSG. The processing gas includesa fluorocarbon gas. The processing gas may further include a rare gas,e.g., Ar gas. In the step ST11, a pressure in the processing chamber 12is set to a predetermined level by the operation of the gas exhaust unit50. Further, in the step ST11, the high frequency power from the firsthigh frequency power supply 62 is supplied to the lower electrode LE.The high frequency bias power from the second high frequency powersupply 64 may be supplied to or may not be supplied to the lowerelectrode LE. In the step ST11, the plasma of the processing gasincluding a fluorocarbon gas is generated and dissociated fluorocarbonis deposited on the surface of the wafer W. As a result, the deposit DPis formed as shown in FIG. 13.

In the step ST11, the processing condition is different from those ofthe steps ST4 and ST5 and the processing condition that realizes adeposition mode, i.e., a mode in which deposition of deposit DP on thewafer W dominates over the etching of the first region R1, is selected.In this example, C₄F₆ gas is used as the fluorocarbon gas in theprocessing gas used in the step ST11.

The step ST11 is executed under the following processing condition.

25

-   Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65    Pa)-   Processing gas

C₄F₆ gas: 2 sccm to 10 sccm

Ar gas: 500 sccm to 1500 sccm

-   High frequency power for plasma generation: 100 W to 500 W-   High frequency bias power: 0 W

Next, the step ST12 is executed in the present embodiment. In the stepST12, a plasma of a processing gas including an oxygen-containing gasand an inert gas is generated in the processing chamber 12. To that end,in the step ST12, the processing gas is supplied into the processingchamber 12 from a gas source selected from the gas sources of the gassource group GSG. In this example, this processing gas includes oxygengas as the oxygen-containing gas. Further, in this example, theprocessing gas includes, as the inert gas, a rare gas such as Ar gas.The inert gas may be nitrogen gas. In the step ST12, a pressure in theprocessing chamber 12 is set to a predetermined level by the operationof the gas exhaust unit 50. In the step ST12, the high frequency powerfrom the first high frequency power supply 62 is supplied to the lowerelectrode LE. In the step ST12, the high frequency bias power from thesecond high frequency power supply 64 may not be supplied to the lowerelectrode LE.

In the step ST12, active species of oxygen are generated and the amountof deposit DP on the wafer W is appropriately decreased by the activespecies of oxygen, as shown in FIG. 14. As a result, the opening in themask MK and the opening formed by the etching are prevented from beingblocked by an excessive amount of deposit DP. In the case of theprocessing gas used in the step ST12, the oxygen gas is diluted with theinert gas. Therefore, the excessive removal of the deposit DP issuppressed.

The step ST12 is executed under the following processing condition.

-   Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65    Pa)-   Processing gas

O₂ gas: 2 sccm to 20 sccm

Ar gas: 500 sccm to 1500 sccm

-   High frequency power for plasma generation: 100 W to 500 W-   High frequency bias power: 0 W

In the present embodiment, the step ST12 in each sequence, i.e., asingle step ST12, is executed for two or more seconds. In the step ST12,the deposit DP can be etched at a rate of 1 nm/sec or less. In the caseof executing the sequence by using the plasma processing apparatus 10,it takes a time to switch gases for shifting the steps ST11 to ST13 fromone to another. Therefore, the step ST12 needs to be executed for two ormore seconds in consideration of time required for stabilization ofdischarge. However, if the etching rate of the deposit DP in the stepST12 is too high, the deposit for protecting the second region R2 may beexcessively removed. Thus, the deposit DP is etched at a rate of 1nm/sec or less in the step ST12. Accordingly, it is possible toappropriately control the amount of the deposit DP on the wafer W. Theetching rate of the deposit DP which is 1 nm/sec or less in the stepST12 can be realized by selecting a pressure in the processing chamber,a degree of dilution of oxygen in the processing gas with a rare gas,i.e., an oxygen concentration, and a high frequency power for plasmageneration from the above-described condition.

Next, in the step ST13, the first region R1 is etched. In the step ST13,a process of promoting reaction between fluorocarbon in the deposit DPand silicon oxide in the first region R1 is performed. To that end, inthe step ST13, a processing gas is supplied into the processing chamber12 from a gas source selected among the gas sources of the gas sourcegroup GSG. The processing gas includes an inert gas. In one example, theinert gas may be a rare gas such as Ar gas. Or, the inert gas may benitrogen gas. In the step ST13, a pressure in the processing chamber 12is set to a predetermined level by the operation of the gas exhaust unit50. Further, in the step ST13, the high frequency power from the firsthigh frequency power supply 62 and the high frequency bias power fromthe second high frequency power supply 64 are supplied to the lowerelectrode LE.

The step ST13 is executed under the following processing condition.

-   Pressure in processing chamber: 10 mTorr (1.33 Pa) to 50 mTorr (6.65    Pa)-   Processing gas

Ar gas: 500 sccm to 1500 sccm

-   High frequency power for plasma generation: 100 W to 500 W-   High frequency bias power: 20 W to 300 W

In the step ST13, the plasma of the inert gas is generated and ions areattracted to the wafer W. Accordingly, the reaction between radicals offluorocarbon included in the deposit DP and silicon oxide of the firstregion R1 is promoted and, thus, the first region R1 is etched. Byexecuting the step ST13, the first region R1 in the recess which isprovided by the second region R2 is etched as shown in FIG. 15.

The sequence SQ may be executed once. In this case, the determination ina step STJ to be described later is not required, and the step ST4 isexecuted after the execution of the sequence SQ.

In the present embodiment, the sequence SQ is repeatedly executed. Inother words, the sequence SQ is executed multiple times. In the presentembodiment, it is determined in the step STJ whether or not a stopcondition is satisfied. It is determined that the stop condition issatisfied when the sequence SQ has been performed a predetermined numberof times. When it is determined in the step STJ that the stop conditionis not satisfied, the sequence SQ is performed again from the step ST11.On the other hand, when it is determined in the step STJ that the stopcondition is satisfied, a step ST4 is executed. The step ST4 of themethod MT2 is the same step as the step ST4 of the method MT when theexecution of the step ST4 is terminated, the wafer W has a state inwhich the first region R1 is etched to the bottom surface of the recessformed by the second region R2 as shown in FIG. 10.

In the method MT2, the sequence SQ is performed when the second regionR2 is exposed and the second region R2 is more reliably protected by thedeposit DP. Then, the first region R1 is etched by radicals in thedeposit DP. Therefore, the erosion of the second region R2 is furthersuppressed.

While various embodiments have been described, the disclosure may bevariously modified without being limited to the above-describedembodiments. For example, the target object to which the methodsaccording to the above-described embodiments is not limited to thetarget object shown in FIG. 2. For example, the methods according to theabove-described embodiments can be applied to any target object havingthe first region of silicon oxide and the second region of siliconnitride.

Further, the methods according to the above-described embodiments can beperformed by using any plasma processing apparatus other than thecapacitively coupled plasma processing apparatus. For example, themethods according to the above-described embodiments may be performed byusing an inductively coupled plasma processing apparatus or a plasmaprocessing apparatus for generating a plasma by a surface wave such as amicrowave.

In the method MT2, the sequence SQ may be executed after the step ST3without executing the step ST5. Further, the sequence SQ may not includethe step ST12. On the other hand, when the sequence SQ includes the stepST12, the execution order of the step ST12 in the sequence SQ may bechanged for example, in the sequence SQ, the step ST12 may be executedafter the step ST13.

Hereinafter, test examples 1 to 3 executed to examine the step ST4 willbe described. In the test examples 1 to 3, there was prepared a wafer WEhaving a state shown in a partially enlarged cross sectional view ofFIG. 16A. The wafer WE includes a protruding region RA formed on thesubstrate SB, a second region R2 made of silicon nitride and coveringthe protruding region RA, and a first region R1 made of silicon oxideand covering the second region R2 while filling the recess formed by thesecond region R2. The recess formed by the second region R2 is a trenchhaving a width of 20 nm and a depth of 150 nm. In comparative examples 1and 2, the same wafer WE was prepared.

In each of the test examples 1 to 3 and the comparative examples 1 and2, the first region R1 was etched under the following processingcondition by using the plasma processing apparatus 10.

<Processing Condition of Test Example 1>

Pressure in processing chamber: 30 mTorr (4 Pa)

Flow rate of C₄F₆ gas: 4 sccm

Flow rate of Ar gas: 1000 sccm

Flow rate of O₂ gas: 5 sccm

Flow rate of Ar gas with respect to flow rate of C₄F₆ gas: 250 times

High frequency power of first high frequency power supply 62: 40 MHz,500 W

High frequency bias power of second high frequency power supply 64: 13MHz, 50 W

Self-bias potential of lower electrode LE: 350V

Negative DC voltage of power supply 70: −300V

Processing time: 10 minutes

<Processing Condition of Test Example 2>

Pressure in processing chamber: 30 mTorr (4 Pa)

Flow rate of C₄F₆ gas: 0.8 sccm

Flow rate of Ar gas: 1000 sccm

Flow rate of O₂ gas: 0.8 sccm

Flow rate of Ar gas with respect to flow rate of C₄F₆ gas: 1250 times

High frequency power of first high frequency power supply 62: 40 MHz,300 W

High frequency bias power of second high frequency power supply 64: 13MHz, 0 W

Self-bias potential of lower electrode LE: 150V

Negative DC voltage of power supply 70: −300V

Processing time: 10 minutes

<Processing Condition of Test Example 3>

Pressure in processing chamber: 30 mTorr (4 Pa)

Flow rate of C₄F₆ gas: 0.2 sccm

Flow rate of Ar gas: 1000 sccm

Flow rate of O₂ gas: 0.2 sccm

Flow rate of Ar gas with respect to flow rate of C₄F₆ gas: 5000 times

High frequency power of first high frequency power supply 62: 40 MHz,120 W

High frequency bias power of second high frequency power supply 64: 13MHz, 0 W

Self-bias potential of lower electrode LE: 50V

Negative DC voltage of power supply 70: −300V

Processing time: 10 minutes

<Processing Condition of Comparative Example 1>

Pressure in processing chamber: 30 mTorr (4 Pa)

Flow rate of C₄F₆ gas: 8 sccm

Flow rate of Ar gas: 1000 sccm

Flow rate of O₂ gas: 10 sccm

Flow rate of Ar gas with respect to flow rate of C₄F₆ gas: 125 times

High frequency power of first high frequency power supply 62: 40 MHz,500 W

High frequency bias power of second high frequency power supply 64: 13MHz, 100 W

Self-bias potential of lower electrode LE: 50V

Negative DC voltage of power supply 70: −300V

Processing time: 10 minutes

<Processing Condition of Comparative Example 2>

Pressure in processing chamber: 30 mTorr (4 Pa)

Flow rate of C₄F₆ gas: 7.6 sccm

Flow rate of Ar gas: 1000 sccm

Flow rate of O₂ gas: 10 sccm

Flow rate of Ar gas with respect to flow rate of C₄F₆ gas: 131 times

High frequency power of first high frequency power supply 62: 40 MHz,300 W

High frequency bias power of second high frequency power supply 64: 13MHz, 0 W

Self-bias potential of lower electrode LE: 150V

Negative DC voltage of power supply 70: −300V

Processing time: 10 minutes

In the test examples 1 to 3 and the comparative examples 1 and 2, SEMimages of the processed wafer WE were obtained and there were measured areduced amount ΔT1 of a film thickness of the second region R2 disposedabove the central portion of the protruding region RA (difference of thefilm thickness of the second region R12 before and after the processing)and a reduced amount ΔT1 of a film thickness of the second region R2disposed at the shoulder portion of the second region R2 (difference ofthe film thickness of the second region R2 before and after processing).As a result, ΔT1 in the test example 1 was 2.4 nm; ΔT2 in the testexample 1 was 6.3 nm; ΔT1 and ΔT2 in the test example 2 were 0 nm; ΔT1and ΔT2 in the test example 3 were 0 nm. Further, ΔT1 in the comparativeexample 1 was 14.7 nm; ΔT2 in the comparative example 1 was 23.9 nm; ΔT1in the comparative example 2 was 11.1 nm; and ΔT2 in the comparativeexample 2 was 17.6 nm. In the comparative example 1, i.e., in theexample in which the etching was performed under the processingcondition that the flow rate of Ar gas was 125 times of the flow rate ofC₄F₆ gas and the self-bias potential was 500V, the second region R2 wasconsiderably eroded and the film thickness of the second region R2 wasconsiderably decreased. In the comparative example 2 using the self-biaspotential lower than that of the comparative example 1, the filmthickness of the second region R2 was decreased by 10 nm or more. Thisis because, in the comparative example 2, the flow rate of Ar gas withrespect to the flow rate of C₄F₆ gas was 131 times which is less than250 times. On the other hand, in the test examples 1 to 3, the reducedamount of the film thickness of the second region R2 was considerablysmall. Therefore, it is clear that in the methods MT and MT2, the firstregion R1 can be etched while suppressing the erosion of the secondregion R2 by executing the step ST4.

While the disclosure has been shown and described with respect to theembodiments, it will be understood by those skilled in the art thatvarious changes and modifications may be made without departing from thescope of the disclosure as defined in the following claims.

What is claimed is:
 1. A method comprising: (a) providing a targetobject including a first region containing silicon oxide and a secondregion containing silicon nitride in a processing chamber of a plasmaprocessing apparatus; and (b) generating a plasma from a processing gascontaining a fluorocarbon gas and a rare gas in the processing chamber,wherein in (b), a self-bias potential of a lower electrode is greaterthan or equal to 4V and smaller than or equal to 350V and a flow rate ofthe rare gas is 250 to 5000 times a flow rate of the fluorocarbon gas inthe processing gas.
 2. The method of claim 1, wherein in (b), a firstgas including a fluorocarbon gas and a rare gas is supplied from a firstgas source into the processing chamber and a second gas including only arare gas or including a fluorocarbon gas and a rare gas at a volumeratio different from a volume ratio of the first gas is supplied from asecond gas source into the processing chamber.
 3. The method of claim 1,wherein in (b), a gaseous mixture of a fluorocarbon gas and a rare gasis supplied from a single gas source into the processing chamber.
 4. Themethod of claim 1, wherein the rare gas is argon gas.
 5. The method ofclaim 1, wherein the processing gas further includes oxygen gas.
 6. Themethod of claim 1, wherein the second region includes a recess and thefirst region fills the recess and covers the second region, the methodfurther comprising: executing a sequence one or more times to etch thefirst region in a period including a time when the second region isexposed, wherein the sequence includes: generating a plasma of aprocessing gas including a fluorocarbon gas in the processing chamberand forming a deposit containing fluorocarbon on the first region andthe second region; and generating a plasma of an inert gas in theprocessing chamber.
 7. The method of claim 6, wherein the sequencefurther includes: generating a plasma of a processing gas including anoxygen-containing gas and an inert gas.
 8. The method of claim 1,wherein the target object includes a substrate; a protruding regionformed on the substrate; the second region covers the protruding regionand includes a recess; the first region fills the recess and covers thesecond region; an organic film formed on the first region; ananti-reflection film formed on the organic film; and a resist maskformed on the anti-reflection film.
 9. The method of claim 8, the methodfurther comprising: (c) etching the anti-reflection film through anopening of the resist mask by generating a plasma from a secondprocessing gas in the processing chamber.
 10. The method of claim 9,wherein the second processing gas contains a fluorocarbon gas.
 11. Themethod of claim 9, the method further comprising: (d) etching theorganic film through an opening of the anti-reflection film bygenerating a plasma from a third processing gas in the processingchamber.
 12. The method of claim 11, wherein the third processing gasincludes hydrogen gas and nitrogen gas, or oxygen gas.
 13. The method ofclaim 11, further including, after (b), etching the first region throughan opening of the organic film which is formed by (d).
 14. A processingapparatus, comprising: a processing chamber having a gas inlet and a gasoutlet; a plasma generator; and a controller configured to cause: (a)providing a target object including a first region containing siliconoxide and a second region containing silicon nitride; and (b) generatinga plasma from a processing gas containing a fluorocarbon gas and a raregas, wherein in (b), a self-bias potential of a lower electrode isgreater than or equal to 4V and smaller than or equal to 350V and a flowrate of the rare gas is 250 to 5000 times of a flow rate of thefluorocarbon gas in the processing gas.